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Make certain you're looking at the correct diagrams. Are you certain you're not confusing what you have with the 5-speed manual or the MazdaSpeed3?
 

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Discussion Starter #22
Make certain you're looking at the correct diagrams. Are you certain you're not confusing what you have with the 5-speed manual or the MazdaSpeed3?
At this point I have no idea. The only thing I do know is I have the P0971 code and that may or may not be related to a trans sensor that may or may not be correct.
 

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Discussion Starter #23
Update:

I replaced the part (FN-01-21-550) that came yesterday this morning and took it for a ride. I didn't get above 40 before the CEL went on with the same P0971 code.

I am at a loss what to do next and having an incredible amount of frustration with this car.
 

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Discussion Starter #24 (Edited)
I did find another video for a different year Mazda 5 that was replacing the VSS for different codes (P0733 & P0744), which was located behind the trans pan on the driver side axle of all places. I guess that would explain the 3 sensors that Mazda references?

No idea what part number that is but should probably pull off that black shield to just make sure it's full plugged in.

Edit: Well it's the exact same part for input shaft speed sensor (FN12-21-551A). I did replace that early on, which didn't fix anything so I winder if I have the original one laying around still.

Edit: Well I did locate the 551A part I replaced a little while ago, which I assume was not actually bad in the first place. May swap it with the one in the pic to see if that helps.

Took a pic.
105481
 

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Discussion Starter #25
So I just swapped out the 3rd sensor near the axle and got same code. I think I give up. The POS Mazda wins. Really not worth taking to dealer to spend a couple grand on something has little value.

So frustrated.
 

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Ok, I took a look at mine and found the sensor in your pic. So instead of the FSM being wrong by showing an extra sensor, it turns out to be just the most misleading diagram ever printed. It shows those 3 sensors all lined up in a row, and there's nothing indicating any of them are not located right on top of the tranny case. Hopefully this information will be a big help to others having speed sensor issues who read this in the future.

I understand your frustration, because this electrical/computer stuff can at times be horribly difficult to figure out (even when all the diagrams are correct and accurate). They did however provide some diagnostic electrical testing, which I mentioned previously. The troubleshooting tree is fairly straightforward, and says to first test the sensor wires at the connectors for power, ground, and signal wire continuity. And if all of that checks out, the last step in the manual is to replace the TCM.

You've done so much work on this already, perhaps after a bit of R&R you might reconsider and at least run those fairly simple electrical tests. And then, if that testing doesn't identify any problem, you can either give up on it, or try the final recommended step and shell out $500 or so for a replacement TCM.
 

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Discussion Starter #27
Ok, I took a look at mine and found the sensor in your pic. So instead of the FSM being wrong by showing an extra sensor, it turns out to be just the most misleading diagram ever printed. It shows those 3 sensors all lined up in a row, and there's nothing indicating any of them are not located right on top of the tranny case. Hopefully this information will be a big help to others having speed sensor issues who read this in the future.

I understand your frustration, because this electrical/computer stuff can at times be horribly difficult to figure out (even when all the diagrams are correct and accurate). They did however provide some diagnostic electrical testing, which I mentioned previously. The troubleshooting tree is fairly straightforward, and says to first test the sensor wires at the connectors for power, ground, and signal wire continuity. And if all of that checks out, the last step in the manual is to replace the TCM.

You've done so much work on this already, perhaps after a bit of R&R you might reconsider and at least run those fairly simple electrical tests. And then, if that testing doesn't identify any problem, you can either give up on it, or try the final recommended step and shell out $500 or so for a replacement TCM.
Honestly, not sure I follow the electrical tests. I should start with getting a multimeter?
 

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Honestly, not sure I follow the electrical tests. I should start with getting a multimeter?
Yes, a MM is the required tool, but no need to buy something expensive - spending around $25 or so from an online site or a box store will be perfectly ok. Once you have the meter, it's not too difficult to run the testing, and I'd be glad to run through it with you.

Just keep in mind that I wouldn't necessarily be expecting a problem with the wires - it could be, but more likely not. It's just that you want to do the simple wiring testing before putting out the big bucks for something like a TCM. Yes, you could just go out and hang on a new TCM without any testing. But how pi$$ed off would you be if then turned out that a wire/connector was bad, instead of the $500 TCM? Always try the easiest, least expensive stuff first, which is usually going to be testing.
 

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Yes. It always boils down to the basics of troubleshooting little items first, as m3iguy says. Follow his directions and I bet you find the culprit.
 

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Yes, a MM is the required tool, but no need to buy something expensive - spending around $25 or so from an online site or a box store will be perfectly ok. Once you have the meter, it's not too difficult to run the testing, and I'd be glad to run through it with you.

Just keep in mind that I wouldn't necessarily be expecting a problem with the wires - it could be, but more likely not. It's just that you want to do the simple wiring testing before putting out the big bucks for something like a TCM. Yes, you could just go out and hang on a new TCM without any testing. But how pi$$ed off would you be if then turned out that a wire/connector was bad, instead of the $500 TCM? Always try the easiest, least expensive stuff first, which is usually going to be testing.
So I have a MM now. Any chance you can walk me through testing like I am a 3rd grader?
 

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Discussion Starter #31
Was watching this video and at 6:30 time frame, he mentions another little sensor next to the 3 prong sensor that was very loose and causing an issue with the TCM. May have to look at that sensor connection as well.

 

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So I have a MM now. Any chance you can walk me through testing like I am a 3rd grader?
First off some new information. In hindsight I should have done this earlier, but anyway I just read the removal procedure for all of the sensors. In that section they did mention removing the metal shield that's in your pic from earlier today. They don't tell you where it is, but it's obvious that it can't be on top of the tranny case. So my bad on that, and I could have saved a bunch of time if I had thought to read that section sooner, because it confirms that there are 3 speed sensors on the vehicle.

And along with that, I now know that they call the one covered by the shield the 'VSS' sensor. So that also means that the other 3 pin sensor (the one closer to the firewall), has to be what they call the 'intermediate sensor' (our old friend). And according to their doc for the P0971, only an issue with the intermediate sensor is what sets that code.

So in order to test that sensor, you will need to remove the connector. Now on my vehicle I can actually remove that connector without needing to get anything else out of the way, via an open space between the other parts, just to the left of the PCM case. So I'll ask you first if you can undo the sensor connector that way on yours as well, because it would save lots of time if you can. Post back the answer, and hopefully it will be yes.
 

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Discussion Starter #33
First off some new information. In hindsight I should have done this earlier, but anyway I just read the removal procedure for all of the sensors. In that section they did mention removing the metal shield that's in your pic from earlier today. They don't tell you where it is, but it's obvious that it can't be on top of the tranny case. So my bad on that, and I could have saved a bunch of time if I had thought to read that section sooner, because it confirms that there are 3 speed sensors on the vehicle.

And along with that, I now know that they call the one covered by the shield the 'VSS' sensor. So that also means that the other 3 pin sensor (the one closer to the firewall), has to be what they call the 'intermediate sensor' (our old friend). And according to their doc for the P0971, only an issue with the intermediate sensor is what sets that code.

So in order to test that sensor, you will need to remove the connector. Now on my vehicle I can actually remove that connector without needing to get anything else out of the way, via an open space between the other parts, just to the left of the PCM case. So I'll ask you first if you can undo the sensor connector that way on yours as well, because it would save lots of time if you can. Post back the answer, and hopefully it will be yes.
I have the connector removed on the 3 prong sensor on top of trans.
 

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I have the connector removed on the 3 prong sensor on top of trans.
Great - that saves time and effort! On to the testing.

First make sure your meter is reading DC voltage correctly by simply touching the meter leads to the 2 battery posts. You should see a reading on the meter display of somewhere around 12.5 volts. (usually 12.3-12.6) Depending on the style of your meter, you might need to fiddle with multiple DC voltage settings, in order to see the battery voltage displaying that 12.5V However, if your meter does auto ranging, then there will be only one DC voltage option.

After you confirm the battery static voltage, you will be probing the 3 female pin sockets in that speed sensor connector you just removed. You will first need to attach the negative meter testing lead to the negative battery terminal - alligator or most any other spring clip will do the job. You need to make sure the metal stays in contact with the post, and check for battery voltage one more time, to make sure the negative lead is making good contact.

Turn the ignition key to the 'ON' position and leave it there. Now find the female pin socket corresponding to the yellow (hot) wire - it's on the outside, left or right, depending on the orientation of the connector. GENTLY probe that yellow wire pin socket with the positive meter lead, and the reading on the meter should nearly the same voltage as at the battery (~12.5V). Now move the meter lead and probe the middle, (red wire) pin socket. The meter reading should be close to 5 volts.

The last test is for the black (ground) wire, and for that test you will need to switch the clipped meter lead at the battery from the negative post, over to the positive post. You can clip the red meter lead instead of the black one, but it really doesn't matter because the readings will just show up as negative valves. Once the meter lead is attached to the battery, probe the other lead to the black wire pin slot, and you should once again see the same battery voltage (~12.5) as before,

Try it and let's see what the readings are.
 

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Discussion Starter #35 (Edited)
Great - that saves time and effort! On to the testing.

First make sure your meter is reading DC voltage correctly by simply touching the meter leads to the 2 battery posts. You should see a reading on the meter display of somewhere around 12.5 volts. (usually 12.3-12.6) Depending on the style of your meter, you might need to fiddle with multiple DC voltage settings, in order to see the battery voltage displaying that 12.5V However, if your meter does auto ranging, then there will be only one DC voltage option.

After you confirm the battery static voltage, you will be probing the 3 female pin sockets in that speed sensor connector you just removed. You will first need to attach the negative meter testing lead to the negative battery terminal - alligator or most any other spring clip will do the job. You need to make sure the metal stays in contact with the post, and check for battery voltage one more time, to make sure the negative lead is making good contact.

Turn the ignition key to the 'ON' position and leave it there. Now find the female pin socket corresponding to the yellow (hot) wire - it's on the outside, left or right, depending on the orientation of the connector. GENTLY probe that yellow wire pin socket with the positive meter lead, and the reading on the meter should nearly the same voltage as at the battery (~12.5V). Now move the meter lead and probe the middle, (red wire) pin socket. The meter reading should be close to 5 volts.

The last test is for the black (ground) wire, and for that test you will need to switch the clipped meter lead at the battery from the negative post, over to the positive post. You can clip the red meter lead instead of the black one, but it really doesn't matter because the readings will just show up as negative valves. Once the meter lead is attached to the battery, probe the other lead to the black wire pin slot, and you should once again see the same battery voltage (~12.5) as before,

Try it and let's see what the readings are.
yellow - 12.02v
red - 4.39v
black - 12.02v

Because the sensor with 3 prongs is the only one that throws the P0791 code and testing the voltage on the connector seems good, we are assuming this now to be a TCM?

I am just a little hesitant that I am not actually getting any codes related to the TCM.
 

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Before moving on to the TCM, I need to ask a couple other questions, because 12.02 and 4.39 are both quite low. First off, is it possible you had the key at the on position for a long time (i.e. hours), which might have drained the battery down? Also, did you see that same 12.02V at the battery posts, at the time you took the readings at the speed sensor connector?

I'm not trying to imply this is a battery problem, because I did read what you said about this problem going on for a year. And that makes it highly unlikely to be caused by a bad battery. But nevertheless, It's important to find the reason for any result that's not what we're expecting to see.
 

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Discussion Starter #37 (Edited)
Before moving on to the TCM, I need to ask a couple other questions, because 12.02 and 4.39 are both quite low. First off, is it possible you had the key at the on position for a long time (i.e. hours), which might have drained the battery down? Also, did you see that same 12.02V at the battery posts, at the time you took the readings at the speed sensor connector?

I'm not trying to imply this is a battery problem, because I did read what you said about this problem going on for a year. And that makes it highly unlikely to be caused by a bad battery. But nevertheless, It's important to find the reason for any result that's not what we're expecting to see.
Voltage at the battery posts with the key in OFF position, I get 12.43 volts.

Voltage at the battery posts with the key in ON position, I get 12.15 volts.

When I tested the plug earlier, the key was in the on position for just a few minutes.
 

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Ok 4.68 on the signal wire does bring that voltage into the 'acceptable' range spec of 4.5 to 5.5. OTOH, the fact that it's on the low end might tend to support the idea that the TCM is the issue, given that the signal wire is connected directly to the TCM. However, there's one additional consideration related to this, which I'll mention after the next paragraph.

So it's now for you to decide if you want to buy a replacement TCM (or perhaps try to find one with the same part number in a pick-and-pull savage yard). I certainly can't tell you it will correct the problem and eliminate the code, only that it's the final action listed in the Mazda diagnostics, following the testing that you have now completed. And I'm also fairly sure it would be what a shop would do at this point as well.

That said, there is actually one more electrical test that still has not been done, and so I'll run that by you just for the sake of completeness. It's a test of the integrity of the signal wire mentioned above, along with the speed sensor connector and the TCM connector. They call it a 'connectivity' test, but I'd check the resistance instead, looking for just 1-2 Ohms. I didn't mention this previously because it's a very short wire, and it's hard to imagine a problem with it. However, corrosion inside of the TCM connector is one other possibility which might be somewhat more likely. And if that situation did exist, it could certainly explain why that signal wire is on the low end of the voltage range.

Unfortunately, running that test would require removing all of the intake and battery stuff, in order to be able to undo the TCM connector. You would of course need to do all of that work if you're going to replace the TCM, but doing the test before buying a replacement TCM would probably mean doing the whole thing twice. I'd guess you wouldn't be very happy to rip it all apart and put it back together for that one test, but your call on that.

And one final thing about what you wrote about there being no TCM codes. Actually the P0791 is a code set by the TCM, when it sees something it doesn't like about that speed sensor input. The catch of course is that the TCM isn't checking itself to see if it is actually the cause of the problem as well. I imagine that degree of error checking would be considered to be way over the top by the auto engineers, but it sure would make it a lot easier to figure this stuff out.
 
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